Re: Short list with things to finish for D2

[KennyTM~]

On Nov 20, 09 04:31, aarti_pl wrote:

Andrei Alexandrescu pisze:

aarti_pl wrote:

aarti_pl pisze:

Andrei Alexandrescu pisze:

2. User-defined operators must be revamped. Fortunately Don already
put in an important piece of functionality (opDollar). What we're
looking at is a two-pronged attack motivated by Don's proposal:

http://prowiki.org/wiki4d/wiki.cgi?LanguageDevel/DIPs/DIP7

The two prongs are:

* Encode operators by compile-time strings. For example, instead of
the plethora of opAdd, opMul, ..., we'd have this:

T opBinary(string op)(T rhs) { ... }

The string is "+", "*", etc. We need to design what happens with
read-modify-write operators like "+=" (should they be dispatch to a
different function? etc.) and also what happens with
index-and-modify operators like "[]=", "[]+=" etc. Should we go
with proxies? Absorb them in opBinary? Define another dedicated
method? etc.

* Loop fusion that generalizes array-wise operations. This idea of
Walter is, I think, very good because it generalizes and
democratizes "magic". The idea is that, if you do

a = b + c;

and b + c does not make sense but b and c are ranges for which
a.front = b.front + c.front does make sense, to automatically add
the iteration paraphernalia.

(..)

Andrei

I kinda like this proposal. But I would rather call template like
below:

T opInfix(string op)(T rhs) { ... }
T opPrefix(string op)(T rhs) { ... }
T opPostfix(string op)(T rhs) { ... }

and allow user to define her own operators (though it doesn't have
to be done now).

I know that quite a few people here doesn't like to allow users to
define their own operators, because it might obfuscate code. But it
doesn't have to be like this. Someone here already mentioned here
that it is not real problem for programs in C++. Good libraries
don't abuse this functionality.

User defined operators would allow easy definition of Domain
Specific Languages in D. I was already writing about it some time ago:

http://www.digitalmars.com/webnews/newsgroups.php?art_group=digitalmars.D&article_id=81026

http://www.digitalmars.com/webnews/newsgroups.php?art_group=digitalmars.D&article_id=81352


BR
Marcin Kuszczak
(aarti_pl)

Of course for opPrefix/opPostfix signatures will be different:
T opPrefix(string op)() { ... }
T opPostfix(string op)() { ... }

Sorry for mistake.

BR
Marcin Kuszczak
(aarti_pl)

I think we'll solve postfix "++" without requiring the user to define
it. Do you envision user-defined postfix operators?

Andrei

Well, maybe something like below:

auto a = 2²; //(quadratic power of 2)
auto a = 5!; //factorial of 5
auto a = 2Ƴ + 3ɛ; //solving equations
auto weight = 5kg; //units of measurement

The point is that this covers whole scope of operators. In fact even
built-in operators could be defined using it.

Postfix operator ++ can be defined using prefix operator++ just by
delegation and this can be default.

Best Regards
Marcin Kuszczak
(aarti_pl)

It will make weird stuff like

class G {
  G opPostfix(string op)() if (op == "%") { ... }
  G opCall(int x) { ... }
}

auto g = new G;
g% (4+2); // what should it do?